I like all of them except the dude because he is scary and I kind of feel like I'll seize if I look at him. My favorite one is the sunflower one because it seems more detailed and more successful because it looks the best.

I think one of the advantages of block paint is that the contrast between black and white reflects the shadow and light, but the disadvantage is that it is hard to create depth. So to me the second and third are the most successful.